Known in the state of the art are measuring devices, in the case of which a so-called oscillatory fork or a single rod or a membrane, as mechanically oscillatable unit, is excited to execute oscillations. Since the oscillations, or their characterizing variables, such as frequency, amplitude and phase, are dependent on the contact with a medium, or on properties of the medium, such as density or viscosity, conclusions regarding the measured variables can be drawn from the characterizing variables of the oscillations. Therefore, such a measuring device permits, for example, the monitoring of fill level or the measuring of density.
It has been found, that there are regions of phase difference between the exciter and the received signal, in which the behavior of the oscillatory system can be influenced. Thus, the detecting of foam can be enabled or suppressed. Furthermore, the dependence of the oscillations on changes of viscosity can be canceled (see DE 100 57 974 A1). In order to achieve these effects, it is, however, required, that the desired phase values be set as exactly as possible. A problem, however, is that the measuring of the phases is not always optimally possible.